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The Atmosphere

The Atmosphere. I. What is air?. --A mixture of gasses. Nitrogen (78%) needed for growth of plants and animals absorbed in the form of nitrates, made by bacteria. Oxygen (21%) needed by animals, produced by plants energy released when it combines with other compounds

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The Atmosphere

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  1. The Atmosphere

  2. I. What is air? --A mixture of gasses

  3. Nitrogen (78%) • needed for growth of plants and animals • absorbed in the form of nitrates, made by bacteria

  4. Oxygen (21%) needed by animals, produced by plants energy released when it combines with other compounds breaks down some elements in rocks by oxidation

  5. Carbon dioxide (.03%) • needed by plants for photosynthesis • important in greenhouse effect

  6. Ozone (a “trace gas”) • a form of oxygen-- O3 • in stratosphere absorbs ultraviolet radiation • at ground level is dangerous pollutant (smog) Argon (0.9%) • inert, does not form compounds

  7. Water vapor (0 to 4%) • only gas that varies much • absorbs heat

  8. G. Trace gases • neon, helium, methane, krypton, xenon, hydrogen, ozone

  9. II. What is the structure of our atmosphere? A. troposphere-- to 11 km, zone where weather occurs B. stratosphere-- 11-50 km, contains ozone layer, where jets fly C. mesosphere-- 50-80 km, coldest layer D. thermosphere-- 80-85 km up, temperatures rise, contains ionosphere and exosphere

  10. III. What role does air pressure play in weather? • Close to the earth atoms & molecules are pushed together because of pressure from mass above therefore greatest at sea level and decreases upward • Differences in air’s density can cause air pressure variations • Barometer measures air pressure, average in millibars is 1013 mb

  11. Highs • Cool air more dense, causes high pressure • Highs are associated with cool dry air—clear skies

  12. Lows • Warmed air less dense, causes low pressure areas • Lows are associated with warm and moist conditions—rain and storms

  13. Air moves from areas of high pressure to areas of low pressure

  14. IV. How does temperature affect the circulation of air in the atmosphere? • Energy supplied by sun • Greenhouse effect keeps heat in troposphere, makes life possible

  15. Heat is reflected by ice, water, snow, sand • Heat is absorbed by vegetation and dark surfaces

  16. Heat is transferred by radiation, conduction, and convection • Convection currents are caused by differences in density between warm and cool fluids • Convection causes air to rise over Equator, sink at Poles

  17. Coriolis effect causes moving objects to be deflected to right in Northern hemisphere, left in Southern)

  18. Unequal heating can also cause movement, as in sea and land breezes

  19. V. How does temperature affect the ability of air to hold moisture? • Warm air “holds more moisture” than cool air • In warm air gas molecules are farther apart- more space for water vapor

  20. Relative humidity is the amount of water in air compared to how much it could hold at that temperature • Air at 100 percent relative humidity is saturated, water may condense from it

  21. May be measured with hygrometer or wet bulb / dry bulb psychrometer

  22. Temperature at which condensation will occur is called dew point

  23. VI. How do clouds form and produce precipitation? • Condensation occurs when • 1. air is cooled below dew point and • 2. condensation nuclei (dust or salt particles) are present • Clouds are collections of tiny water droplets suspended in air

  24. At a certain size they fall as precipitation • Snow is formed by water vapor turning directly to solid

  25. VII. What are the names and characteristics of common cloud types? Cloud families • 1. cirrus-- high, white, feathery, ice clouds, also called “mare’s tails”

  26. 2. cumulus-- thick, puffy, “fair weather clouds”

  27. 3. stratus -- clouds in layers

  28. 4. nimbus-- produce precipitation

  29. Clouds also classified by height • Stratus clouds close to ground are called “fog”

  30. VIII. What is the significance of air masses to weather? An “air mass” is body of air that has characteristic properties

  31. Properties depend on where mass originated

  32. From air mass, air flows down and spirals out clockwise, causing anticyclone (fair) Air pushes into low pressure areas, spiraling in counterclockwise cyclone (stormy weather)

  33. IX. How do fronts influence the weather? • Boundary between air masses is called a front

  34. Warm front • 1. Warm air mass meets cold air mass • 2. Warm air slides up over cold air in long wedge • 3. Nimbostratus clouds form and may cause precipitation over long period

  35. Cold front • 1. Cold air mass meets warm air mass • 2. Cold air forces warm air up along steep front • 3. Showers and thunderstorms result

  36. Stationary front causes weather to remain the same over long time Occluded front when two cool air masses trap warm air between them, causing high winds and precipitation

  37. X. How is weather portrayed on weather maps? Local collecting stations contribute data in form of station models

  38. Weather maps show • 1. isobars, lines connecting points of equal pressure

  39. 2. isotherms- line connecting points of equal temperature

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